1. Field of the Invention
This invention relates to a method and system for ethanol production, and more specifically, this invention relates to an integrated method and system for producing ethanol from synfuel and methanol feedstocks.
2. Background of the Invention
Ethanol, and the production of ethanol, falls into and out of favor in discussions related to energy independence, national security, and environmental responsibility.
Much of current research focuses on optimizing petroleum feedstock infrastructures by additives for easy incorporation with gasoline, diesel fuel, and jet fuel. However, the natural progression of liquid energy development is toward fuels derived from feedstocks from renewable resources (such as biomass), or solar-based processes.
Biomass-derived fuels include highly oxygenated moieties (e.g. alcohols) and are typically derived from renewable sources and sources comprised mainly of relatively less complex molecules. These sources include wood, paper, and other municipal bio-oriented waste.
Solar based fuels are those produced from carbon dioxide and water using energy. Energy costs to produce solar fuels remain high.
Methanol is a primary transportation fuel. Current methods for producing methanol include the use of catalysts in combination with syn gas. Liquid phase catalysts and solid phase catalysts have been used. Liquid phase processes for producing methanol were developed using coal as a feedstock. Lastly, using natural gas as a feedstock for producing methanol is only technically feasible, given methane's growing importance as a power plant fuel to supplant dirtier coal-fire facilities.
Currently, the primary technology for producing methanol is via the reaction of syngas with a solid phase fixed bed catalyst. This is because liquid entrained methanol catalyst to produce methanol is considered less efficient than solid phase fixed bed catalyst use.
Furthermore, state of the art methanol production sequences are equilibrium limited, which is to say that the presence of methanol often results in the reaction reversing or shifting back to the left. The decomposition of methanol to syn gas (reverse reaction) occurs because the chemistry is limited to the carbon-containing the oxygen atom (single carbon compound). Thus, H2 is lost to form a CH2O, which can then loose H2 to form CO and H2, (i.e., syn gas, the starting reactants). Conversion of syn gas to methanol is significantly limited at relatively low temperatures because of thermodynamics. That is why some processes run under high pressure conditions to “liquefy the product” to drive the reaction to higher conversion. (i.e. Le Chatlier's Principle)
Decomposition of ethanol and higher alcohols also occurs at the oxygen-containing carbon. The alkyl carbons, CH3, in the case of ethanol, tend to react with H2 to form methane during the “reverse” reaction process. As such, the reaction of ethanol to syn gas is essentially irreversible under these reaction conditions.
Also, methanol's drawbacks are formidable and include its toxicity, corrosiveness, and higher volatility.
Ethanol is a safer alternative as a transportation fuel. Ethanol can be derived from synfuels just as methanol. For example, U.S. Pat. No. 4,476,334, held by the instant Assignee, discloses a method for producing ethanol from synfuel by producing methanol or methanol formate as intermediate reactants. However, this process requires that methanol first be produced in a separate step, and then recovered via an energy intensive distillation process. Any ethanol subsequently produced is also separated via distillation.
A need exists in the art for a method and a system for producing ethanol. The method and system should utilize renewable feedstocks such as biomass and municipal solid waste. Further, the method should integrate the chemistry of methanol production to minimize additional capital outlays and energy expenditures.